Lesson 3: Topological Spin Transport & Entanglement in Quantum Materials
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 Speaker

Stephan Roche
Institut Català de Nanociència i Nanotecnologia (ICN2), Barcelona, Spain  When

2024/07/16
11:30  Place
 DIPC seminar room
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I will present theoretical spin transport features in MoTe_{2} and WTe_{2}based materials which are particularly interesting Quantum Materials. By focusing on the monolayer limit, using DFTderived tightbinding models, and using both efficient bulk and multiterminal formalisms and techniques [14], I will show the emergence of new forms of intrinsic spin Hall effect (SHE) that produce large and robust inplane spin polarizations. Quantum transport calculations on realistic device geometries with disorder demonstrate large chargetospin interconversion efficiency with gate tunable spin Hall angle as large as θ_{xy}≈80%, and SHE figure of merit λ_{s}.θ_{xy}∼810 nm, largely superior to any known SHE material [1]. I will also show our theoretical prediction of an unconventional canted quantum spin Hall phase in the monolayer T_{d}WTe_{2}, which exhibits hitherto unknown features in other topological materials [2]. The low symmetry of the structure induces a canted spin texture in the yz plane, dictating the spin polarization of topologically protected boundary states. Additionally, the spin Hall conductivity gets quantized (2e^{2}/h) with a spin quantization axis parallel to the canting direction. We have predicted the control of the canted QSHE by electric field [3]. I will also present some recent results on very large spinorbit torque phenomena in Janus transition metal dichalcogenide materials and other topological features [4].
I will finally discuss the role of entanglement between intraparticle degrees of freedom in spin transport and dynamical patterns of entanglement, as enabling novel platform for generating and manipulating quantum entanglement between internal and interparticle degrees of freedom [5].
References
 Vila, C.H. Hsu, J.H. Garcia, L.A. Benítez, X. Waintal, S. Valenzuela, V. Pereira, S. Roche, “ChargetoSpin Interconversion in LowSymmetry Topological Materials”, Physical Review Research 3, 043230 (2021)
 H. Garcia, M. Vila, C.H. Hsu, X. Waintal, V.M. Pereira, S. Roche, “Canted Persistent Spin Texture and Quantum Spin Hall Effect in WTe_{2, }Physical Review Letters 125 (25), 256603 (2020)
 JH Garcia, J You, et al. S. Roche, “ Electrical control of spinpolarized topological currents in monolayer Physical Review B 106 (16), L161410 (2022)
 Vojacek et al. submitted to Physical Review Letters; J. Medina Dueñas et al, unpublished.
 BG de Moraes, AW Cummings, S Roche, “Emergence of intraparticle entanglement and timevarying violation of Bell's inequality in Dirac matter”, Physical Review B 102 (4), 041403 (2020); J. Martinez, A.W. Cummings and S. Roche arXiv preprint arXiv:2310.17950